1. Field of the Invention
The present invention relates generally to the field of computer security, especially relating to electronic records.
2. Description of Related Art
Modern technology has profoundly changed the way business transactions are conducted today. The use of computers and other data processing devices are now commonplace in both large and small businesses. The connectivity provided by intranets and the Internet have reduced information transfer times from days down to seconds. For a reasonable investment, small businesses and even non-profit organizations can acquire communications benefits similar to those of large high-technology corporations.
Governments, too, have taken advantage of the cost and time savings benefits offered by electronic communications. Electronic filing of U.S. income tax returns is now the preferred method of filing a return by the U.S. government. Transferring documents electronically eliminates postage and shipping charges and allows documents to be received at their destination almost instantaneously.
In recognition of the general acceptance of using electronic communications in the business place, laws regulating electronic communications have begun to be developed and adopted. More laws are likely to come about, or existing laws revised, as acceptance of electronic communications continues to grow and become more highly developed in the future.
The purpose of laws, such as the Uniform Electronic Transactions Act (UETA) and the e-Sign Act, is to validate the authority of electronic transactions to legally bind one party to another party, and to provide a legal framework for enforcement.
The system described in this patent application is a system for secure, enforceable electronic communications.
An understanding of several industry-standard definitions is necessary to be able to evaluate the importance of this system and compare it with other solutions currently available or that may become available as the use of electronic business transactions continues to increase.
An electronic transaction is any type of business that is conducted by electronic means, such as by computer, Personal Device Assistants (PDAs), and other devices not yet invented. For example, the transaction may consist of ordering a book or other product from a Web site and making payment by electronic means, such as providing credit card information or debiting the payment from a checking account.
An electronic record, according to the Electronic Signatures in Global and National Commerce Act (E-Sign), is “a contract or other record created, generated, sent, communicated, received, or stored by electronic means.”1 The E-Sign Act further states that a record must be retrievable in perceivable form.2 
A repository is the secure environment in which electronic records are maintained. The repository must encompass sufficient security methods to ensure safe storage and integrity of the electronic record.
An electronic signature is “an electronic sound, symbol, or process attached to or logically associated with a contract or other record and executed or adopted by a person with the intent to sign the record.”3 
A message digest is a compressed representation of an electronic record. Message digests are produced using standard, published, one-way hashing algorithms. Message digests produced by the same algorithm generally are the same length in bits. The message digest will be considered a unique valid representation of the electronic record because it is computationally infeasible for two different electronic records to produce the same message digest while using the same message digest function.
Message digest algorithms currently on the market, such as MD-2, MD-4, MD-5, SHA-1, and SHA-256, take specific portions of the record (512 bits or 1024 bits) and create a message digest of that portion. This hash of the set length of bits produces a set of hex chain values. The chain values are summed bitwise along with a seed value to produce the final message digest. For SHA-1, as an example, five 32-bit chain values are produced for each 512 bits of data. A full history of Public Key Cryptography (PKC) systems is described in W. Diffie's, “The First Ten Years of Public-Key Cryptography,” which is incorporated herein by reference.
A digital signature is a form of electronic signature, generated by computer hardware or software and represented in a computer as a string of binary digits. The methods of producing a digital signature involve a set of rules and a set of parameters such that the digital signature produced is unique and verifiable. Both the identity of the signatory (person represented by the digital signature) and the integrity of the data (binary bits making up the digital signature) can be verified. Today, the first step in generating a digital signature is typically the generation of a message digest, usually much smaller than the electronic record on which it is based. The message digest will be unique because it is computationally infeasible for two different electronic methods to produce the same message digest on the same electronic record; therefore, the use of a message digest as a representation of the electronic record is considered valid. The second step in generating a digital signature is to cryptographically combine the message digest and an asymmetric private key. Standards for generation of digital signatures will be known to those of ordinary skill in the art.
A Public Key Cryptography (PKC) system is an asymmetric encryption system, meaning that it employs two keys, one for encryption and one for decryption or validation of what is encrypted. Asymmetric systems adhere to the principle that knowledge of one key (the public key) does not permit derivation of the second key (the private key). Thus, PKC permits the user's public key to be posted, in a directory or on a bulletin board for example, without compromising the user's private key. This public key concept simplifies the key distribution process. Popular PKC systems make use of the fact that finding large prime numbers is computationally easy but factoring the products of two large prime numbers is computationally infeasible. Example PKC algorithms are the Digital Signature Algorithm (DSA)4, the Rivest, Shamir, and Adleman (RSA) algorithm, as specified in Internet Engineering Task Force (IETF) Request for Comments (RFC) 2347 and its successors.
A private key is the half of a Public Key Cryptography (PKC) pair that is kept private and secret, and is used to generate a digital signature.
A public key is the half of a PKC pair that is published, and is used to verify a digital signature. Each person involved in an electronic transaction based on the private and public key method of digital signature generation and verification will possess a private and public key pair. A public key may be known to the public in general, but a private key is never shared. Anyone can verify a person's digital signature by using that person's public key, but only the possessor of a person's private key may generate a digital signature. More information about how public keys and private keys work is contained later in this section.
Typically, public and private keys are used as the means of allowing for the generation and verification of digital signatures. Public-key encryption schemes, commonly called PKC, are well known and utilize a public key and a private key that are mathematically related. Based on a public-key/private-key pair, digital messages can be encrypted by either of the keys and decrypted by the other, with the public keys recorded in a public directory, which is publicly accessible, and the private key privately retained. Typically, the signer of the message accesses the public-key directory and retrieves the receiver's public key. Then the signer encrypts the message with the receiver's public key, and conveys the encrypted message to the receiver. The receiver, upon receiving the encrypted message, decrypts the message with his private key.
PKC can also be used to generate a digital signature to authenticate the signer. Typically, the signer creates a message digest of the electronic record. After generating the message digest, the signer creates a digital signature from the message digest with his private key. The receiver, upon receiving the digital signature and the message, uses the signer's public key to verify the signature. This process is performed iteratively until the entire electronic record has been hashed. This operation ensures the identity of the signer because he is the only person who can encrypt the message with his private key.
Besides the PKC method, another encryption method is the symmetric algorithm. An example of this is the Data Encryption Standard (DES), which is described in Data Encryption Standard, Federal Information Processing Standards Publication 46 (1977) (“FIPS PUB 46,” and its successors) that are available from the U.S. Department of Commerce. In general, a symmetric cryptographic system is a set of instructions, implemented in either hardware, software, or both, that can convert plain text into ciphertext, and vice versa. In a symmetric cryptographic system, a specific key is used that is known to the users but is kept secret from others.
A blue ink signature is a physically-produced signature made by a person using an ink pen, regardless of the color of the ink or the legibility of the signature. An “X” or a scribble can suffice as a legally-binding signature provided that both parties involved in the transaction have agreed upon the existence of an ink mark in a particular area or areas of the physical record constitutes agreement by the signer to the terms contained within the physical record. When the agreement states that a witness or notary public must observe and verify that the signer did intend to demonstrate agreement to the terms of the physical record by placing an ink signature, or mark, in the appropriate areas, then the signature and/or stamp of a witness or notary public must be present on the physical record in order for the transaction to be legal and enforceable.
A person is defined as “an individual, corporation, business trust, estate, trust, partnership, limited liability company, association, joint venture, governmental agency, public corporation, or any other legal or commercial entity.”5 
An authoritative copy is the best available copy of a document. The best available document may indeed be the original, but when an exact original cannot be found, then the best available copy of a document becomes the authoritative copy. The authoritative copy must be clearly identifiable as an authoritative copy. Thus, the authoritative copy must be associated with a means of establishing, identifying, maintaining, and enforcing control of the authoritative copy.
Current law has established that senders and receivers of transferable electronic records have rights equal to those of senders and receivers of equivalent paper records.
The significance of current acts such as the Electronic Signatures in Global and National Commerce Act (E-Sign) and the Uniform Electronic Transactions Act (UETA) is that electronic records, exchanged between two parties who have agreed to conduct a transaction by electronic means, and with the ability for the electronic records to be retrieved by both parties, shall be valid, legal transactions enforceable just as if they contained “blue ink” signatures. “Retrieved,” as used in the preceding sentence, means the document must be able to be stored and printed by the receiver.
Computers and other electronic devices, such as Personal Digital Assistants (PDA) and cellular telephones, provide the interface terminals from which parties to a business transaction may take advantage of the many benefits of electronic communications. One of the most important benefits of electronic communications is the ability to communicate and transact business with a person, or groups of people, almost anywhere in the world. Electronic communications can take place over telephone lines, the Internet, and through the air via cellular and satellite communication systems.
Computers, and other electronic devices, receive digital information into their memory and present the information to a user. The information can be present in different ways, such as visual displays, voice and other audio output through a speaker, and by printing the information. A combination of the output methods, commonly referred to as multimedia, is intended to enhance the user's understanding of the communicated information. Computers and other electronic devices can display information in the form of text, graphs, pictures, and video.
It should be understood that for purposes of this patent application, we are defining an electronic transaction environment as any technology that allows two computers to communicate with each other. Thus, the words electronic and digital are essentially interchangeable. A network, intranet, or The Internet is not necessary; for example, a PDA could communicate with a standalone computer using infrared signalling. The process of retrieving files from one computer or interface terminal device (such as a PDA) to another is called downloading. The process of sending files to another computer or interface terminal is called uploading.
Computers and hardware alone are not sufficient to complete electronic transactions. Software is also needed to provide for security between the transacting parties and to allow the parties to digitally sign electronic records.